What Are Silicon Carbide and Tungsten Carbide?
Silicon carbide (SiC) and tungsten carbide (WC) are the two hard materials that form the rubbing face pair of a mechanical seal. Silicon carbide, a ceramic compound, offers the highest hardness and thermal conductivity; tungsten carbide, bonded by a metal phase, is far tougher and resists impact and edge chipping.
The face pair governs seal life more than any other component: leakage starts there, friction heat is generated there and wear progresses there. The material decision follows directly from the fluid analysis.
This guide compares the two silicon carbide grades, the binder options for tungsten carbide, carbon graphite and alumina ceramic, then maps pairs to fluids and explains the DIN 24960 / EN 12756 codes. For seal designs, see mechanical seal types.
Silicon Carbide Grades: Sintered SSiC and Reaction-Bonded RBSiC
Sintered silicon carbide (SSiC) is pressureless sintered so that no free silicon remains. With no soluble metallic phase, it stays stable across practically the whole pH range, in strong acids and caustic solutions. Hardness is approximately 2,500 HV, the highest among seal faces.
Reaction-bonded silicon carbide (RBSiC or SiSiC) is made by infiltrating a porous carbon skeleton with molten silicon, leaving roughly 8-15% free silicon. That phase is vulnerable to strong alkalis, hot caustic and hydrofluoric acid, but the grade is cheaper and easier to produce in large geometries.
Both grades conduct heat almost like metals, so friction heat leaves the face quickly and thermal shock behavior is good. Choose SSiC for strong alkalis, caustic cleaning cycles and high-purity processes; RBSiC suffices for clean water and neutral industrial fluids.
Tungsten Carbide: Cobalt Versus Nickel Binder
Tungsten carbide is a cermet made by sintering hard WC grains with a metallic binder. At approximately 1,500 HV its hardness stays below silicon carbide, but its fracture toughness is markedly higher, so a tungsten carbide seal face suits heavy-duty pumps with vibration, cavitation and hydraulic shock.
The binder determines corrosion behavior. A cobalt-bonded grade is tougher and cheaper, but in acidic media the cobalt dissolves selectively and grains break out of the face. A nickel-bonded grade resists acids and seawater far better, at somewhat lower strength.
Tungsten carbide is also dense, raising rotating mass and cost on large diameters. Its thermal conductivity is high but below silicon carbide, so it is usually paired with SiC at very high PV values. Product data lists a tungsten carbide face for MEGASEAL models such as MS-7.
Carbon Graphite: Self-Lubrication and Impregnation Types
Carbon graphite, with its layered structure, is the only seal face material that lubricates itself. Friction is low, it conforms to the mating face and it tolerates short dry runs far better than any hard face. Being soft, it embeds small particles but wears quickly under heavy particle load.
The porous carbon skeleton is sealed by impregnation, which sets the chemical and temperature limits. Resin-impregnated grades cover general water and chemical duties; antimony-impregnated grades carry higher pressure and temperature and resist blistering better.
Carbon graphite always works against a hard mating face. A hard-soft pair delivers low friction and low leakage, while two hard faces are reserved for abrasive media. For elastomers and metallic components, see material selection for sealing products.
Alumina Ceramic: Economical Face With a Thermal Shock Limit
Alumina ceramic (Al₂O₃) is the most economical hard face material, and hardness rises with purity. It is stable in oxidizing media and clean water, but lacks the wide working window silicon carbide offers in strong acids and alkalis.
Its weak point is thermal conductivity. Because friction heat leaves the face slowly, alumina is sensitive to thermal shock: a sudden temperature change or a brief dry run can start a crack. Silicon carbide replaces it wherever PV is high or dry running is possible.
Paired with carbon graphite, alumina serves well in clean water and low-pressure duties where cost governs.
Seal Face Materials Compared
The table below is a qualitative screening tool; the figures are approximate ranges from engineering literature, to be confirmed with the manufacturer.
| Property | SSiC (Q1) | RBSiC (Q2) | Tungsten carbide (U) | Alumina (V) | Carbon graphite (A/B) |
|---|---|---|---|---|---|
| Hardness | Very high (≈ 2,500 HV) | Very high (≈ 2,200 HV) | High (≈ 1,500 HV) | Medium-high | Low |
| Thermal conductivity | Very high | Very high | High | Low | Medium |
| Chemical resistance | Very high, full pH range | High; limited in strong alkalis and HF | Medium with cobalt binder, high with nickel | High; good in oxidizing media | Set by the impregnant |
| PV limit | Very high | High | High | Medium | Medium; mating face dependent |
| Abrasive fluids | Very suitable | Suitable | Suitable | Limited | Not suitable |
| Thermal shock | Good | Good | Good | Poor | Very good |
| Toughness and impact | Low (brittle) | Low (brittle) | High | Low (brittle) | Medium |
| Relative cost | High | Medium | High | Low | Low-medium |
Which Face Pair Suits Which Fluid?
Face pair selection starts with the particle load, lubricity and chemical aggressiveness of the fluid; pressure and speed narrow it further. One side should normally be softer, and two hard faces are reserved for abrasive media.
| Face pair | Typical fluid and condition | Selection rationale |
|---|---|---|
| SiC / SiC (Q1/Q1 or Q2/Q2) | Abrasive particles, slurry, mining and pulp lines | Particles cannot embed and wear stays low, but dry running is not tolerated |
| SiC / carbon graphite (Q1/B) | Clean water, general-purpose pumps and chemical processes | Low friction, low power loss and low leakage |
| WC / carbon graphite (U/B) | Heavy-duty pumps: vibration, hydraulic shock, viscous fluids | Tungsten carbide toughness prevents edge chipping |
| WC / SiC (U/Q1) | High pressure and high face loading | Toughness plus high thermal conductivity |
| Alumina / carbon graphite (V/A) | Clean water, low-pressure domestic and garden pumps | Economical when the fluid is clean and loads low |
| SSiC / SSiC (Q1/Q1) | Fluids containing strong alkalis, caustic or hydrofluoric acid | No free silicon to attack |
DIN 24960 and EN 12756 Material Codes
DIN 24960 and EN 12756 identify face and elastomer materials with letter codes, the common language of orders and spare parts. The binder assignments below reflect common usage in published code lists and should be confirmed with the manufacturer.
| Code | Material | Typical use |
|---|---|---|
| Q1 | Sintered silicon carbide (SSiC) | Abrasive and chemically aggressive fluids |
| Q2 | Reaction-bonded silicon carbide (RBSiC) | General industrial fluids, economical hard face |
| U1 | Tungsten carbide, cobalt binder (common usage) | High impact and vibration with a neutral fluid |
| U2 | Tungsten carbide, nickel binder (common usage) | Acidic media and seawater |
| A | Antimony-impregnated carbon graphite | Higher pressure and temperature, blistering risk |
| B | Resin-impregnated carbon graphite | General-purpose water and chemical duties |
| V | Alumina ceramic (Al₂O₃) | Clean water and economical low-load duties |
Face Materials in Meccanotecnica Umbra Turkey Series
Meccanotecnica Umbra Turkey is the Turkish company of the Italian mechanical seal manufacturer Meccanotecnica Umbra S.p.A. From Ikitelli OSB, Istanbul, it manufactures and supplies mechanical seals, gland packings, gaskets and rotary joints for automotive, home appliance and industrial pump applications.
The table lists face materials and limit values from product data. Silicon carbide and carbon graphite are shared across the industrial series; tungsten carbide and ceramic faces appear on MEGASEAL models.
| Series | Face materials (product data) | Limit values |
|---|---|---|
| DPS | SiC, carbon | 12 bar, -20 to 180 °C; DIN 24960 / EN 12756 compliant |
| DRM1-S | SiC, carbon | 16 bar, -20 to 180 °C; conical spring, direction-dependent |
| HUHNSEAL | SiC, carbon | 25 bar, -40 to 260 °C; single and double cartridge |
| MS-7 | SiC, tungsten carbide, carbon | 25 bar, -50 to 220 °C; EN 12756, 14-200 mm shaft |
| DR2-S | SiC, carbon | 30 bar, -30 to 220 °C; protected multi-spring, balanced |
Face Material Selection Checklist
Six questions narrow the decision; once answered, usually only one suitable face pair remains.
- Does the fluid carry abrasive particles? If so, a two-hard-face SiC/SiC pair is required.
- What is the pH range? With strong alkalis, hot caustic or HF, choose SSiC over RBSiC.
- Are acids or seawater present? Specify a nickel-bonded rather than cobalt-bonded tungsten carbide.
- Is there a dry-running risk? Carbon graphite tolerates short interruptions; alumina and two-hard-face pairs (SiC/SiC, WC/SiC) do not, so choose a carbon mating face.
- Is the pressure-velocity product high? A silicon carbide face removes friction heat fastest.
- Is there vibration or hydraulic shock? Tough tungsten carbide is safer than a brittle ceramic.
Continue With the Right Face Pair
For face and elastomer options and technical PDFs by series, browse the product catalog; share your fluid data and operating point and we decide the combination together.
